(d) The motion of proton is magnetic field will be circular. $v = 2\pi rf$ $\ \ \ = 2 \times 3.14 \times 50 \times 10^{- 2} \times 10 \times 10^{6}$ $\ \ \ = 3.14 \times 10^{7}\ m/s$
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Ph.D. in Physics with 19+ years of teaching experience.